Subtle and gradual changes in the female reproductive system cause its function to decline in older females, until no further reproductive capacity remains. This period of declining function furnishes a useful model system to study the nature of aging changes at a tissue and cellular level. Our studies will include measurement of steroid hormones and gonadotropic hormones. The uptake and metabolism of the steroid hormones by the uterine tissue will also be compared between young and old females, with a goal of clarifying the nature of the subtle changes that seem to occur in uterine function. Ultrastructural studies will be done to determine the very early cell changes in uterine response to hormones, comparing local and systemic treatment at different ages. As unilateral ovariectomy causes accelerated reproductive failure in the functional uterine horn, this model system will be used for study of the uterine changes. Attempts to improve function by various means of hormone treatment, local vs. systemic, will also be tried. Methods to be used include radioimmunoassay of hormones, biochemical analysis of uteri, and ultrastructural, histochemical, and autoradiographic study of uteri as they respond to steroid hormones.